Pulmonary Hypertension:
Primary pulmonary hypertension (PPH) is a fatal disease causing progressive right heart failure within three years after diagnosis. Recently, various pathophysiological changes associated with this disorder, including vasoconstriction, vascular remodelling (i.e. proliferation of both media and intima of the pulmonary resistance vessels), and in situ thrombosis have been characterized (e.g.: D'Alonzo, G. E., Bust, R. J., Ayres, S. M. et al. Survival in patients with primary pulmonary hypertension. Results from a national prospective registry. Ann. Intern. Med. 115, 343-349. Sep. 1, 1991; Palevsky, H. I., Schloo, B. L., Pietra, G. G. et al. Primary pulmonary hypertension. Vascular structure, morphometry, and responsiveness to vasodilator agents. Circulation 80, 1207-1221. 1989; Rubin, L. J. Primary pulmonary hypertension. N. Engl. J. Med. 336, 111-117. Jan. 9, 1997; Wagenvoort, C. A. and Wagenvoort, N. Primary pulmonary hypertension: a pathological study of the lung vessel in 156 clinically diagnosed cases. Circulation 42, 1163-1184. 1970; Wood, P. Pulmonary hypertension with special reference to the vasoconstrictive factor. Br. heart J. 20, 557-570. 1958). Impairment of vascular and endothelial homeostasis is evidenced from a reduced synthesis of prostacyclin (PGI2), increased thromboxane production, decreased formation of nitric oxide and increased synthesis of endothelin-1 (Giaid, A. and Saleh, D. Reduced expression of endothelial nitric oxide synthase in the lungs of patients with pulmonary hypertension. N. Engl. J. Med. 333, 214-221. 1995; Xue, C. and Johns, R. A. Endothelial nitric oxide synthase in the lungs of patients with pulmonary hypertension [letter]. N. Engl. J. Med. 333, 1642-1644. Dec. 14, 1995). The intracellular free calcium concentration of VSMC of pulmonary arteries in PPH has been reported to be elevated. The therapy of pulmonary hypertension is unsatisfactory. Current therapy involves calcium cannel blockers and prostacyclins. Although the vasodilation in numerous tissues, heart and lung tissue included, there is no clinical evidence up to now that VIP or PACAP are effective in the treatment of pulmonary hypertension in humans. The invention describes for the first time the clinical relevance of VIP, PACAP and compounds having the biological activity of VIP or PACAP for the treatment of primary pulmonary hypertension (PPH), secondary pulmonary hypertension (SPH), and arteriolar hypertension associated with PPH.
Arterial Hypertension:
Comparable to the pulmonary circulation, endothelial cells of the systemic circulation release both relaxing and contracting factors that modulate vascular smooth muscle tone and also participate in the pathophysiology of essential hypertension. Endothelium-dependent vasodilation is regulated primarily by nitric oxide but also by an unidentified endothelium-derived hyperpolarizing factor and by prostacyclin. Endothelium-derived contracting factors include endothelin-I, vasoconscrictor prostanoids, angiotensin II and superoxide anions. Under physiological conditions, there is a balanced release of relaxing and contracting factors. The balance can be altered in cardiovascular diseases such as hypertension, atherosclerosis, diabetes and other conditions, thereby contributing to further progression of vascular and end-organ damage. In particular, endothelial dysfunction leading to decreased bioavailability of nitric oxide impairs endothelium-dependent vasodilation in patients with essential hypertension and may also be a determinant for the premature development of atherosclerosis. Different mechanisms of reduced nitric oxide activity have been shown both in hypertensive states and several cardiovascular diseases, and endothelial dysfunction is likely to occur prior to vascular dysfunction.
VIP and PACAP are synthesized in various components of the central nervous system, e.g. specific brain regions like hippocampus and cortex as well as in the pituitary gland and peripheral ganglia. VIP is furthermore secreted by immune cells and by some neoplastic cells (e.g. pancreatic cancer).
Vasoactive Intestinal Peptide (VIP):
VIP is a 28 amino acid peptide consisting of the following amino acid sequence (from N- to C-terminal): His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Asn-Ser-Ile-Leu-Asn (SEQ ID No. 1).
Healthy individuals exhibit low concentration of VIP (<40 pg/ml serum). VIP is a widely distributed peptide hormone which mediates a variety of physiological responses including gastrointestinal secretion, relaxation of gastrointestinal vascular and respiratory smooth muscle, lipolysis in adipocytes, pituitary hormone secretion, and excitation and hyperthermia after injection into the central nervous system. Under physiologic conditions VIP acts as a neuroendocrine mediator. Some recent findings suggest that VIP also regulates growth and proliferation of normal as well as malignant cells (Hultgardh, Nilsson A., Nilsson, J., Jonzon, B. et al. Growth-inhibitory properties of vasoactive intestinal polypeptide. Regul. Pept. 22, 267-274. 1988). The biological effects are mediated via specific receptors (VIP-R) located on the surface membrane of various cells (Ishihara, T., Shigemoto, R., Mori, K. et al. Functional expression and tissue distribution of a novel receptor for vasoactive intestinal polypeptide. Neuron 8, 811-819. 1992). VIP may exert stimulating and trophic effects on neoplastic cells from neuroblastoma, breast, lung and colon cancer (e.g. Moody et al., Proc. Natl. Acad. Sci. USA, 90, 4345, 1993), inducing its own receptors by feedback mechanisms. In some cases VIP produced dose-dependent stimulation of mitosis (Wollman et al., Brain Res., 624, 339, 1993). VIP and biologically functional analogues and derivatives thereof are shown to have vascular smooth muscle relaxant activity (Maruno, K., Absood, A., and Said, S. I. VIP inhibits basal and histamine-stimulated proliferation of human airway smooth muscle cells. Am. J. Physiol. 268, L1047-L1051, 1995), hair growth activity, apoptosis activity enhanced sustained bronchodilation activity without remarkable cardiovascular side effects, and are effective against disorders or diseases relating to bronchial spasms including asthma, some cases of hypertension, impotence, ischaemia, dry eye and mental disorders, such as Alzheimer's disease (see e.g. WO 9106565, EP 0536741, U.S. Pat. No. 3,880,826, EP 0204447, EP 0405242, WO 9527496, EP 0463450, EP 0613904, EP 0663406, WO 9735561, EP 0620008).
VIP receptor has been detected on airway epithelium of the trachea and the bronchioles. It is also expressed in macrophages surrounding capillaries, in connective tissue of trachea and bronchi, in alveolar walls, and in the subintima of pulmonary veins and pulmonary arteries.
Pepidergic nerve fibers are considered the source of VIP in the lungs (e.g.: Dey, R. D., Shannon-WA, Jr, and Said, S. I. Localization of VIP-immunoreactive nerves in airways and pulmonary vessels of dogs, cat, and human subjects. Cell and Tissue Research 220, 231-238. 1981; Said, S. I. Vasoactive intestinal polypeptide (VIP) in asthma. Ann. N.Y. Acad. Sci. 629, 305-318. 1991). VIP decreases the resistance in the pulmonary vascular system (e.g.: Hamasaki, Y., Mojarad, M., and Said, S. I. Relaxant action of VIP on cat pulmonary artery: comparison with acetylcholine, isoproterenol, and PGE1. J. Appl. Physiol. 54, 1607-1611. 1983; Iwabuchi, S., Ono, S., Tanita, T. et al. Vasoactive intestinal peptide causes nitric oxide-dependent pulmonary vasodilation in isolated rat lung. Respiration 64, 54-58. 1997; Saga, T. and Said, S. I. Vasoactive intestinal peptide relaxes isolated strips of human bronchus, pulmonary artery, and lung parenchyma. Trans. Assoc. Am. Physicians. 97, 304-310. 1984). Further studies show a high rate of VIP-R expression in the lung which is reflected in a high uptake of radiolabeled VIP in the lung of PPH patients who were injected 99 mTc-VIP (e.g.: Raderer, M., Kurtaran, A., Hejna, M. et al. 123I-labelled vasoactive intestinal peptide receptor scintigraphy in patients with colorectal cancer. Br. J. Cancer 78, 1-5. 1998; Raderer, M., Kurtaran, A., Yang, Q. et al. Iodine-123-vasoactive intestinal peptide receptor scanning in patients with pancreatic cancer. J. Nucl. Med. 39, 1570-1575. 1998; Raderer, M., Kurtaran, A., Leimer, M. et al. Value of peptide receptor scintigraphy using (123)I-vasoactive intestinal peptide and (111)In-DTPA-D-Phe1-octreotide in 194 carcinoid patients: Vienna University Experience, 1993 to 1998. J. Clin. Oncol. 18, 1331-1336. 2000; Virgolini, I., Kurtaran, A., Raderer, M. et al. Vasoactive intestinal peptide receptor scintigraphy. J. Nucl. Med. 36, 1732-1739. 1995).
Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP):
PACAP is a neuropeptide isolated from the ovine hypothalamus consisting of the following 38 amino acid residues containing sequence (from N- to C-terminal): His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr-Ser-Arg-Tyr-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Ala-Ala-Val-Leu-Gly-Lys-Arg-Tyr-Lys-Gln-Arg-Val-Lys-Asn-Lys (SEQ ID No. 2).
Two forms of the peptide have been identified: PACAP-38 and the C-terminally truncated PACAP-27. PACAP-27 that shares 68 percent homology with VIP has the following sequence (from N- to C-terminal): His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr-Ser-Arg-Tyr-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Ala-Ala-Val-Leu (SEQ ID No. 3)
PACAP is very potent in stimulating adenylate cyclase and thus increasing adenosine 3,5-cyclic monophosphate (cAMP) in various cells. The compound functions as a hypothalamic hormone, neurotransmitter, neuromodulator, vasodilator, and neurotrophic factor. The major regulatory role of PACAP in pituitary cells appears to be the regulation of gene expression of pituitary hormones and/or regulatory proteins that control growth and differentiation of the pituitary glandular cells. These effects appear to be exhibited directly and indirectly through a paracrine or autocrine action. PACAP plays an important role in the endocrine system as a potent secretagogue for adrenaline from the adrenal medulla. The compound also stimulates the release of insulin. The stage-specific expression of PACAP in testicular germ cells during spermatogenesis suggests its regulatory role in the maturation of germ cells. In the ovary, PACAP is transiently expressed in the granulosa cells of the preovulatory follicles and appears to be involved in the LH-induced cellular events in the ovary, including prevention of follicular apoptosis. In the central nervous system, PACAP acts as a neurotransmitter or a neuromodulator. More important, PACAP is a neurotrophic factor that may play a significant role during the development of the brain. In the adult brain, PACAP appears to function as a neuroprotective factor that attenuates the neuronal damage resulting from various insults. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, and respiratory and urogenital tracts. Two types of PACAP binding sites have been characterized. Type I binding sites exhibit a high affinity for PACAP (and a much lower affinity for VIP), whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes. These are the PACAP-specific PAC1 receptor, which is coupled to several transduction systems, and the two PACAP/VIP-indifferent VPAC1 and VPAC2 receptors, which are primarily coupled to adenylyl cyclase. PAC1 receptors are particularly abundant in the brain and pituitary and adrenal glands whereas VPAC receptors are expressed mainly in the lung, liver, and testes.
Vascular Tone:
The vascular tone is regulated by a complex network of vasoactive effector substances produced either locally in the endothelium, in vascular smooth muscle cells (VSMC), in extrinsic and intrinsic nerves, and by the vascular blood flow itself. In addition to sympatic and parasympatic nervous pathways, neuropeptides from the peripheral nervous system also appear to play an important role in the regulation of vascular tone. One of the most important pathways for the regulation of vascular tone is the production of nitric oxide by the endothelial nitric oxide synthetase (ecnos, NOS III).